The original acute cardiac ischemia (ACI) predictive instrument provides the ED clinician with a 0-100% probability value that a given patient has true ACI, i.e. either unstable angina pectoris or acute myocardial infarction (AMI), as an aid to decision-making for coronary care unit (CCU) admission. Our Multicenter ACI Predictive Instrument Trial (NCHSR/AHCPR # R01 HS02068) demonstrated a 30% reduction in CCU admissions for patients who did not have ACI, with no decrease in appropriate CCU admissions of patients with ACI. However, the original instrument's requirements for a hand-held calculator hampered its acceptance, and it was not applicable to retrospective case review. Our newer "ACI-TIPI" has several improvements. It is "time-insensitive", i.e. it provides the same probability value for a patient whether used in the real-time ED clinical setting or at a later time in medical record review. Its predictive performance has advantages over the original instrument that may help reduce inadvertent discharges of AMIs to home. In addition, incorporated into a computerized electrocardiograph so that the patient's probability of ACI and supporting text are automatically printed on the electrocardiogram header, it is much more attractive for use in the busy clinical setting (and can also be a vehicle for generating computerized feedback and clinical operations reports). The now-proposed TIPI Impact Trial aims to test, in a multicenter 17,500-patient controlled prospective clinical trial, the impact of the ACI-TIPI electrocardiograph on: 1) reducing unnecessary non-ACI CCU admissions; 2) reducing mistaken ED discharges to home of patients with ACI (especially AMI); 3) reducing the number of AMI-related complications by improved triage performance; 4) reducing time from ED presentation to triage; and 5) reducing time to the ED use of thrombolytic therapy for AMI. The structure and size of the trial and the diversity of its ten study site hospitals should yield valid and generalizable results. If successful, the trial will demonstrate an effective and easy-to-use method for improving the triage and treatment of the over five million patients per year presenting to U.S. EDs with symptoms suggestive of ACI and will provide a model of medical practice improvement applicable to many other clinical problems.